In the Diesel engine, there is adopted as one fuel injection system a common rail system which has an integral construction of an injection pump and a nozzle and which uses a fuel injection nozzle (or unit injector) mounted for each cylinder on a cylinder head so that a fuel under a relatively high pressure is accumulated in a common rail acting as a pressure chamber and is boosted to a higher level by a pressure intensifying piston constituting a fuel injection pump and injected by the fuel injection nozzle.
In this common rail system, as shown in FIG. 3, the fuel in a fuel tank 11 is boosted by a fuel feed pump 3 to a pressure level, which is controlled by a pressure control valve 10 controlled by a controller 13, and is stored in a common rail 4 acting as an accumulator. The fuel in this common rail 4 is injected through fuel pipes 5 and solenoid valves 14 into combustion chambers 15 by fuel injection nozzles 6. The quantities and timings of the fuel injections are adjusted by turning ON/OFF the solenoid valves 14 by the controller 13 which receives signals from a variety of sensors 12.
In this case, all the fuel pipes 5 for connecting the discharge ports 7 of the common rail 4 and the fuel injection nozzles 6 have to be given equal lengths so as to prevent dispersion in the pressure responses among the fuel injection nozzles 6, i.e., to prevent the fuel injection timings from going out order.
In the fuel injection system of the common rail system of the prior art, however, the fuel feed pump and the common rail 4 are arranged not with any overlap but planarly on the upper face of the cylinder body 2, as seen from top plan views of an engine 1 shown in FIGS. 4 and 5.
Since the fuel pipes 5 connecting the common rail 4 and the fuel injection nozzles 6 have to be arranged to bypass the fuel feed pump 3, therefore, they have long and different lengths.
In order to feed the fuel under a constant pressure to the fuel injection nozzles 6, on the other hand, each fuel pipe 5 has to be extended to have the longest length so as to make the pressure losses and responses uniform. This necessity elongates the fuel pipes 5 as a whole to complicate the assembling and repairing works. Since the whole lengths of the fuel pipes 5 from the common rail 4 acting as a pressure source to the fuel injection nozzles 6 are increased, moreover, there arises a problem that the responsiveness to the injection pressure is accordingly degraded.
These fuel pipes 5 have to be made of thick and strong metal pipes sufficient for enduring high pressure and vibration so that they are arranged on the vibrating engine 1 to feed the fuel under the high pressure. If the fuel pipes 5 are elongated for that reason, there arises a problem that the fuel pipes 5 provides an unnegligible increase in their total weight.
For these reasons, the fuel pipes 5 between the common rail 4 and the fuel injection nozzles 6 to be used have to be as short as possible for lightening the engine.
In the method for mounting the common rail 4 and the fuel feed pump 3, moreover, there are individually required the brackets for mounting the fuel feed pump 3 on a cylinder body 2 and the brackets for mounting the common rail 4 on the cylinder body 2. This necessity also raises a problem that it causes an increase in the engine weight.
The invention has been conceived to solve the above-specified problems with the engine of the prior art, and has an object to provide a fuel injection system for a Diesel engine, which is enabled to have a small space, a reduced number of parts, a light weight and an excellent reparability by arranging such a common rail as eliminates the bracket structures for the common rail and the fuel feed pump and as makes the fuel pipes short as a whole.